南海北部ODP 1144站中更新世气候转型期有孔虫稳定同位素古气候意义

Paleoclimatic Instability During the Mid-Pleistocene Transition: Implications from Foraminiferal Stable Isotope at ODP Site 1144,Northern South China Sea

中更新世气候转型期是第四纪古气候研究的一个特殊时期。利用大洋钻探ODP184航次在南海北部钻取的1144站时间分辨率高达约290年的沉积物样品，开展中更新世气候转型期古气候变化的研究。在中更新世距今80～100万年前，浮游和底栖有孔虫壳体的稳定氧碳同位素变化揭示出，中更新世气候转型中心，即中更新世革命0．9Ma左右，南海北部表层海水温度的降低和降水量的增加指示东亚冬、夏季风增强。以中更新世革命为界，水体垂向结构上温跃层和营养跃层的深度从之前的间冰期较浅转变为之后的间冰期较深，底层水与表层水的垂直温度梯度从冰期时较大转变为冰期时较小。轨道尺度上，冰消期时南海北部的表层水、次表层水和底层水的变化几乎是同时发生的，不存在超前或滞后的相位差。千年尺度上，有孔虫的氧碳同住素变化都呈现出非常明显的约0．8ka和约1．4ka的气候波动周期。氧同位素0．8ka滤波显示出：在中更新世气候转型期，较强的信号主要出现在间冰期，有时也出现在冰期，与晚第四纪千年尺度气候波动主要出现在冰期不同，说明中更新世的气候转型不仅表现在轨道尺度的气候周期变化上，同时也体现在千年尺度气候波动的特征变化中。

The mid-Pleistocene climate transition （MPT） is a period in geologic history marked by a gradual change in climate periodicity from 40 ka to 100 ka at approximately 0.9 Ma BP, around the marine isotope stages （MIS） 22/23 boundary. Here we present a high resolution record （ - 290 a sampling interval） of foraminiferal stable isotopes during 0.8 - 1.0 Ma at this site. Our data indicated that the Asian monsoon strengthened after the MPT, resulting a deepened thermocline. The depth of the thermocline （DOT） and the nutrientcline were found to be deeper during the glacials than in interglacials before the MPR. After the MPR, the DOT and the nutrientcline became deeper in interglacials than in glacial periods. On the orbital time scale, the surface water change synchro- nized with the bottom water change. However, on the millennial time scale, spectral analysis of foraminiferal oxy- gen and carbon isotope data revealed dominant periodicities at - 0.8 ka and - 1. 4 ka, indicating the climatic instability during the MPT. Furthermore, the amplitude changes of the millennial-scale climate instability were amplified after 0.9 Ma. Most of the strong cyclic signals occurred during the interglacials during the MPT, which is different from the millennial climatic instability during the later Pleistocene. Therefore, our isotopic results confirm the previous conclusion of color reflectance （CR） analysis at this site.